1. Field of the Invention
The present invention relates to a toner which is used for developing an electrostatic latent image formed by an image forming method such as electrophotography. In addition, the present invention also relates to an image forming apparatus producing images using a toner, such as copiers, facsimiles and printers.
2. Discussion of the Background
In electrophotography, images are typically formed by the following method:    (1) an image bearing member such as photoreceptors is charged with a charger (charging process);    (2) imagewise light irradiates the charged image bearing member to form an electrostatic latent image on the image bearing member (light irradiating process);    (3) the electrostatic latent image is developed with a developer including a toner to form a toner image on the image bearing member (developing process);    (4) the toner image is transferred onto a receiving material optionally via an intermediate transfer medium (transfer process);    (5) the toner image is fixed on the receiving material by a fixing device upon application of heat, pressure and/or the like (fixing process); and    (6) toner particles remaining on the image bearing member even after the transfer process are removed by a cleaner so that the image bearing member can be ready for the next image forming processes.
Recently, images formed by electrophotography are requested to have high image qualities (especially, good image reproducibility) whether the images are monochrome images or color images. In particular, in full color images half tone images typically have a large image area proportion. In attempting to produce high quality color images having good evenness and good color reproducibility, toners having a small particle diameter and/or a spherical form have been proposed and developed.
Published unexamined Japanese Patent Applications Nos. (hereinafter JOPs) 2002-148863, 05-313416 and 02-148046 have disclosed methods for manufacturing a toner which include the following processes:    (1) mother toner particles including at least a binder resin and a colorant are dispersed in water or an aqueous solvent including a dispersant to prepare a dispersion;    (2) a mixture of a softening solvent which can soften the mother toner particles, and an organic solvent which can be mixed with water or the aqueous solvent and the softening solvent is added to the dispersion so that the mother toner particles absorb the softening solvent; and    (3) the softening solvent is removed from the mother toner particles.
By using these methods, spherical toners with a proper particle diameter distribution can be prepared while a variety of resins can be used as the binder resin.
However, the toners prepared by these methods have a drawback in that toner particles tend to invade into a gap between an image bearing member (e.g., photoreceptor) and a cleaner because of easily roll (i.e., having an excessive rolling property), thereby causing a cleaning problem in that undesirable streak images are produced in the resultant images. In addition, the toners have a drawback in that when a dot image is developed and transferred, toner particles in a dot image scatters around the dot image due to their excessive rolling property, resulting in occurrence of fogging.
In addition, JOPs 61-22354, 06-250439 and 09-68823 have disclosed toners which include toner particles including a colorant and a binder resin, wherein the toner particles have a volume average particle diameter of from 3 to 9 μm and a specific particle diameter distribution.
By using these toners having a small particle diameter, images having good evenness can be produced without causing a background development problem in that the resultant images have background fouling due to undesirable charge properties of the toners.
However, the toners have a drawback in that toner particles tend to invade into a gap between a photoreceptor and a cleaner in the cleaning process, resulting in occurrence of the cleaning problem. In addition, when the toners have an irregular form, the toners do not cause the cleaning problem, but another problem occurs in that the resultant images have poor fine line reproducibility because toner particles move differently when toner images are formed and transferred.
In addition, JOP 2002-207317 discloses a toner having a flat form. The toner is prepared by the following method:    (1) resin particles having an average primary particle diameter of from 10 to 500 nm is subjected to a salting-out/fusion treatment to prepare secondary particles of the resin; and    (2) the secondary resin particles are flattened to prepare the flat toner.
By using this flat toner, high image-density and high quality images having smooth surface can be produced without causing the fogging problem.
However, the toner has poor fluidity, and thereby the toner particles cannot be densely and uniformly arranged in a dot toner image. Therefore, when images are formed at a high dot (or linear) density, the toner images have poor dot reproducibility.
Because of these reasons, a need exists for a toner which can produce high quality images without causing the fogging problem and without deteriorating fine dot reproducibility.